This invention relates to a propeller vane structure for a marine propulsion unit and more particularly to a propeller construction for fluid streams.
As is well known, a propeller functions by having blades that are disposed at an angle to the direction of fluid flow past them and which generate a fluid flow upon their rotation. Propellers of this type are used in a wide variety of applications including in so called water jet propulsion units wherein the impeller draws water through a water inlet and discharges it through a discharge nozzle for propelling an associated water craft. One problem particular to propeller constructions is the fact that, due to a wide variety of reasons, cavitation can result at the base of the propeller blade and where it is connected to the hub. This cavitation can be caused by the pressure variations attendant to the actual rotation of the blade and the differences in angle to the fluid being pumped or because of the way fluid is delivered to the blade from the fluid inlet. In either event, these pressure variations at the base of the blade can cause erosion of the material of the blade and, accordingly, obvious problems.
This problem is also prevalent in connection with stationery blades such as the straightening blades of a jet propulsion unit or stators. That is, the flow across these blades also tends to cause uneven pressures which can cause cavitation even around the base of the stationery blades.
It is, therefore, a principal object of this invention to provide an improved blade construction for a fluid flow system.
It is a further object of this invention to provide a blade construction for a fluid flow system wherein the base of the blade is supplied with pressurized fluid under all conditions to avoid cavitation.
It is a further object of this invention to provide a blade construction for a fluid system wherein cavitation is precluded at the area where the blade joins the hub.